Mainstream science maintains that humans stopped evolving about 50,000 years ago. Civilization put an end to this process. Therefore, the human of the pre-modern era is the human of today and will be the human tomorrow, right?

Not so fast, say scientists Gregory Cochran and Henry Harpending.

In The 10,000 Year Explosion, they argue that humankind is evolving even faster in the modern age. We developed new genetic traits as recently as the Middle Ages. The Ashkenazi (or European) Jews, for instance, don’t just seem smarter; they actually demonstrate a genetic predisposition toward higher intelligence.

Cochran and Harpending open the book by disputing the common perception of evolution as an inexorably slow process. Natural selection, they assert, does not always transpire over the course of multiple millennia. In fact, an evolutionary leap can be quite fast under certain conditions where organism and challenging environment converge. Such a combination can result in an explosion of genetic variation, especially when species intermingle, as humans interbred with Neanderthals thousands of years ago.

Such explosions and experiments aren’t well represented in fossil records and so mainstream science has regarded them as little more than interesting anomalies. Today, say Cochran and Harpending, genetics is showing that these incidents of chromosomal blossoming — whether due to species interbreeding or behavioral factors such as the change in diet — can impact the genetic future of an entire species in remarkable ways.

One need only look to domesticated variations of the same species to see how evolutionary divergence can take place over just a few hundred years. For instance, stand a tiny Maltese — a somewhat ill-tempered purse dog — up against a Neapolitan Mastiff, or try to make a corn casserole with an ear of teosinte, the genetic ancestor to maize, and you’ll immediately get a sense of how quickly human-aided evolution moves.

While it is true that domesticated animals and plants arise from artificial selection, the process by which certain genes are favored and gradually increase in frequency is, according to the authors, “the essence of evolutionary change.” From a genetic point of view, there exists no important distinction between natural and artificial selection. Genes are genes.

In the same way we selectively breed dogs, so we are selectively (but not as deliberately) breeding ourselves, turning our descendants into crossbreeds. The difference is that, when it comes to human breeding, we have no idea what we’re doing. The sorts of jobs we enter into, the types of social experiences we have, the advice we take about who to marry and how to eat, each of these little decisions and actions — carried out repeatedly over multiple generations — will have effects that show up in the genome.

The Case of Ashkenazi Jews.

Cochran and Harpending single out the Ashkenazi Jews as a textbook example of how cultural decisions from just a few hundred years ago (a nanosecond in the conventional view of evolution) have already resulted in new genetic advantages. Prior to the Middle Ages, Ashkenazi Jews lived in the middle of an important cultural route, linking Europe to key parts of Asia. The Jews were the recipients of tremendous genetic variety as ancient people crossed through their territory, settled down, married, or just mated.

“The Ashkenazi (or European) Jews, for instance, don’t just seem smarter; they actually demonstrate a genetic predisposition toward higher intelligence.” As increasing numbers of Jews moved into Europe during the Middle Ages, cultural rules against marrying outside the group, coupled with external social pressures, resulted in a relatively closed genetic circle. The more useful chromosomal traits picked up in the Levant rose to the top as genetic of dilution was contained. More importantly, the difficult conditions in Europe ensured a strong biological imperative to adapt and survive.

Indeed, while most Europeans experienced the Middle Ages as a clear improvement over the preceding “Dark Age,” European Jews were roundly persecuted and, by and large, locked out of land-ownership. They developed a set of shared survival tactics that happened to be ideally suited for the changes sweeping the continent.

Without the legal ability to own large tracts of land, most were relegated to towns and hamlets. This gave them a head start on urban life. The primary occupations available to the Jews who settled in these nascent urban centers were service trades requiring literacy and arithmetic skills. Abstract intelligence and reasoning skills were valued more highly within the group than was the ability to wield an ax or pull a cart. Over the course of multiple generations, a cultural emphasis on developing quantitative intelligence rather than physical strength accentuated one particular genetic trait at the expense of others. The chosen trait in question was intelligence.

“The [genetic] mutations themselves suggest this,” the authors write. “Some of them look like IQ boosters, considering their effects on the development of the central nervous system.”

Ashkenazi Jews show slightly elevated levels of sphingolipids, a class of fat molecule. Sphingolipids are common in neural tissues and play an important role in signal transmission. Elevated levels of this molecule can lead to more interneural connections, therefore, a bit more brain.

The authors go on to show that people of European Jewish descent, regardless of family background, perform better than average on IQ tests. They are disproportionately well represented among lists of major math and science award winners. Although they account for less than 3% of the U.S. population, they comprise 27% of U.S. Nobel Prize winners over the past two generations, account for about a fifth of CEOs, and about 22% of Ivy League students.

In broaching this idea, Cochran and Harpending flirt with dangerous territory.

The politically sensitive reader is likely to recoil at the notion of genetic variation along ethnic lines resulting in superior intelligence, even if the beneficiaries of this genetic bounty are God’s chosen. All of modern history, Josef Mengele’s genetic experiments on twins in particular, cautions against wading too deeply into such a line of inquiry. Much time and energy has gone into portraying the mere consideration of such distinctions as inherently misguided, pseudoscientific, and even evil.

But this is cultural baggage and has no bearing on the scientific merits of Cochran and Harpending’s argument, per se.

In terms of the future, the value of Cochran and Harpending’s book is primarily as a cautionary tale for our times. We stand today on the verge of yet another great evolutionary leap forward. In the next 50 years, scientists may be able to eliminate all congenital illnesses known to man. Tomorrow’s genomic breakthroughs, treatments, and vaccines will indeed be a great boon to future generations.

But as Cochran and Harpending show, no species can be perfected. In striving to optimize our genetic makeup, we may inadvertently (or even intentionally) decrease the genetic variety that has been vital to our species’ progress. This next evolutionary leap will rise not from the unconscious biological imperative to adapt but from human curiosity as to what improvements may be practically achievable, what, indeed, “improvement” even means. In undertaking this experimentation, we may do well by our descendants to err on the side of chaos, randomness, and nature every now and again.

About the Reviewer: Patrick Tucker is the senior editor of THE FUTURIST and director of communications for the World Future Society.